1. BY Dustin Dela Cruz and Miguel Cabrera

2.  All land plants evolved from aquatic green algae  Land plants, is a very broad term that even includes plants that returned to aquatic habitats  Plants now are everywhere and are 100% essential to life, as they provide food, oxygen, and homes for almost all organisms

3.  Researchers have found that green algae called charophyceans are the closest relatives of land plants  While there are many similarities between green algae and plants, charophyceans share four key trait that suggest the closest relationship between these groups

4.  Rose-shaped complexes for cellulose synthesis ◦ Non-charophyceans made their cellulose with proteins, the difference indicating independent evolution  Peroxisome enzymes ◦ Help minimize the loss of organic products as a result of photorespiration  Structure of flagellated sperm ◦ Sperm with a form of locomotion present in both species  Formation of a phragmoplast ◦ While only in certain Charophyceans, formation of a phragmoplast occurs in all land plants. The phragmoplast is an essential detail of cell division helping with development of cytoskeletal elements

5.  An international initiative was conducted called “Deep Green” in which genes of plants and algal species were analyzed in order to study the transition from algae to plant  They found that Charophyceans were the closest relatives of plants through morphological and biochemical data

6.  Sporopollenin - prevents exposed zygotes from drying up and dying  A very logical assumption would be that Charophyceans gained such traits that allowed them to permanently live on land, which offered huge benefits such as…  rich soil  bright sunlight  abundant CO2

7.  Plant kingdom – researchers are currently debating whether the boundaries of the plant kingdom should be expanded to include the charophyceans and the streptophyta kingdom  Until that is sorted out, the name of the taxon remains kingdom Plantae

8.  1.) The Apical Meristem  Plants need light and CO2 to live, but they can’t move from ground to surface. They can however grow their roots and shoots  Apical meristem – these are localized regions of cell division, at the tips of shoots and roots ◦ Allows for intake of both sunlight and CO2 via the roots and leaves that are produced from the apical meristem

9.  Alternation of generations - The life cycle of all land plants alternate between two different multicellular bodies, with each form able to produce the other  The two multicellular body forms that alternate in the life cycles of land plants are the gametophyte and sporophyte generations ◦ Gametophytes are formed through the mitosis of haploid gametes that fuse during fertilization, then through mitotic division of the zygote, a sporophyte is formed that then can make spores, which form back into gametophytes

10.  The sporophyte has multicellular organs called sporangia that produce plant spores.  In a sporangium, diploid cells called sporocytes go through meiosis and make haploid spores

11.  Gametangia – multicellular organs that produce gametes  Archegonia - Female Gametangia shaped like a vase that produces a single egg retained in the base of the organ  Antheridia – male gametangia that produce and release their sperm into the environment

12.  Multicellular plant embryos develop from zygotes retained in the tissue of the mother, they provide the developing embryo with nutrients  The embryo has specialized placental transfer cells, which enhance the transfer of nutrients from parent to embryo though elaborate ingrowths in the walls surface  This derived trait is so significant that land plants are also known as embryophytes.

13.  The origin of plants is was somewhat of a mystery in terms of when exactly the oldest plant lived  There are fossils that are up to 475 millions years old of spores, however, these spore are very strange, in that they are fused together in groups, and were most likely made by a now extinct species of algae  Through later molecular data by Michael Sanderson of U of Cali., an estimate of around 490-425 million years ago was when the first plants lived

14.  Bryophytes are represented by three phyla of small herbaceous ◦ liverworts(phylum hepatophyta) ◦ Hornworts(phylum anthocerophyta) ◦ Mosses (phylum bryophyta)  Liverworts and hornworts are named for their shape  Mosses are the most familiar bryophytes  Bryophyta is the formal taxonomic name for the phylum that consists only of mosses

15.  The gametophytes are larger and longer- living than sporophytes, ◦ The sporophytes are typically present only part of the time  If bryophyte spores are dispersed to a favorable habitat they may germinate and grow into gametophytes  Bryophyte gametophyte generally form ground hugging carpets and are a few cells thick

16.  Bryophyte sporophytes are usually green and photosynthetic when young, they cannot live independently  They remain attach to their parental gametophytes ◦ They absorb sugars, amino acids, minerals, and water  A typical sporophyte consists of a foot, a seta, and a sporangium

17.  Archegonia develop at the tips of female gametophytes. Antheridia develop on the tops of male gametophytes.  Sperm fertilizes eggs in the archegonia forming a zygote, which develops into an embryo, which grows into a sporophyte— a tall filament with a sporangium at its tip. The sporophyte obtains its nutrients from the female gametophyte.  diploid cells undergo meiosis to produce haploid spores. As the sporangium matures and dries out, its lid pops open. Spores spill out and are carried away by the wind.

18.  Vascular plants dominate most landscapes today  The sperm of ferns and all other seedless vascular plants are flagellated and must swim through a film of water to reach eggs as in bryophytes  Living seedless vascular plants are most common in damp environments

19.  Life cycles with a dominant sporophyte ◦ Fossils suggest that the ancestors of vascular plants had life cycles that were characterized by gametophytes and sporophytes ◦ Among extant vascular plants, the sporophyte generation is larger and more complex  Transport in xylem and phloem ◦ Vascular plants have two types of vascular tissue: xylem which produces most of the water and minerals, and the phloem which includes living sugar-producing cells arranged in tubes that distribute organic products

20.  Evolution of roots ◦ Lignified vascular tissue also provide benefits below ground. ◦ Roots evolved in almost all vascular plants ◦ Roots are organs that anchor vascular plants and enable them to absorb water and nutrients from the soil ◦ Root tissues of living plants closely resembles stem tissues of early vascular plants  Evolution of leaves ◦ Leaves are organs that increase the surface area of vascular plants. Thus capturing more solar energy for photosynthesis ◦ Leaves can be classified either microphylls, which are small spine shaped leaves with a single vein, or megaphylls which are leaves with a highly branched vascular system

21.  Living seedless vascular plants form tow clades ◦ Lycophytes which include club mosses, spike mosses and quillworts ◦ Pterophytes which includes ferns, horsetails and whisk ferns and their relatives

22.  Most ferns produce a single type of spore that gives rise to a bisexual gametophyte  The fern spore develops into a small photosynthetic gametophyte  A variety of mechanisms promote cross fertilization between gametophytes  Sperm use flagella to swim to egg  Zygote is developed into a sporophyte and grows from its parent into a gametophyte  On the underside of the sporophyte, leaves are spots called sori. Each sorus is a cluster of sporangia

23.  While the relationship between bryophytes (like the liverworts, hornworts, and mosses) and vascular plants is still being debated, they still share some important derived traits, like multicellular embryos and apical meristems. However, bryophytes lack many innovations that vascular plants gained.  The accumulation of these traits lead vascular plants to dominate the current earth, as they consist of 93% of all plant species.  While two of the clades that comprise of vascular plants are seedless, they are not monophyletic, because the third clade consists of seed plants.

24.  Seed – an embryo packed with a supply of nutrients inside a protective coat  The majority of living plant species are seed plants; there are two categories of seed plant  Gymnosperms- “naked seed” plants, their seeds are not enclosed in chambers  Angiosperms- the vast majority of seed plants making up a huge clade consisting of flowering plants. These seeds develop inside chambers called ovaries.